Vibration actuator, and lens barrel and camera provided with same

ABSTRACT

A vibration actuator that is easy to manufacture and has good driving performance, and a lens-barrel and a camera provided with the same. The vibration actuator is provided with an oscillator that generates oscillations; and a relative movement member that is pressure contacts the oscillator, and moves relative to the oscillator due to the oscillation. Either a contact face of the oscillator with respect to the relative movement member or a contact face of the relative movement member with respect to the oscillator is a thermosetting resin film that is formed of polyamide-imide resin and fluororesin, and the other contact face is an anodic oxide film.

CORRESPONDING APPLICATIONS

This application claims priority to U.S. application Ser. No.13/577,461, which is in turn a National Stage of PCT/JP2011/052621,filed Feb. 8, 2011. Priority is also claimed to Japanese PatentApplication No. 2010-025160, filed Feb. 8, 2010.

TECHNICAL FIELD

The present invention relates to a vibration actuator, and to a lensbarrel and camera provided with the same.

BACKGROUND ART

In the prior art, vibration actuators are known, which have anoscillator where an electromechanical conversion element and an elasticbody are joined. The vibration actuators generate a progressiveoscillatory wave (below referred to as progressive wave) at the elasticbody by utilizing the expansion and contraction of the electromechanicalconversion element. This progressive wave causes a relative movementmember which is in pressure contact with the oscillator (elastic body)to be frictionally driven. In this type of vibration actuator, a highlyelastic material, for example a metal material of stainless steel familyor the like, is used for the elastic body in order to efficientlytransmit the applied vibrations to the relative movement member.

In such a vibration actuator, frictional contact faces of the oscillatorand the relative movement member exert a large effect on the stability,efficiency, and the like of the driving of the vibration actuator.Therefore, various attempts have been made to improve the durability andthe like of the frictional contact faces.

For example, Patent Document 1 discloses a technique of providing athermosetting resin film on driven faces (namely, frictionallycontacting faces) of a driving body of a rotor and a stator.

Patent Document 1: Japanese Unexamined Patent Application No.2009-232622

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

For example, in the case of using a thermosetting resin film on one ofthe frictional contact faces of an oscillator and a relative movementmember, and using an anodic oxide film on the other, it is possible toreduce noise when driving and improve the abrasion resistance and thelike.

However, due to differences in the hardness between the anodic oxidefilm and the thermosetting resin film, abrasion occurs after endurancetesting, and the starting characteristics may be degraded, accordingly.Further, depending on the type of a thermosetting resin, it may have ahigh coefficient of water absorption. Accordingly, it may occur thatunder high temperature and high humidity environments, it deterioratesto adhere and driving is not properly performed.

In the technique disclosed in Patent Document 1, an anodic oxide film isapplied to the sliding faces of the stator and the rotor. An anodicoxide film is a hard film principally composed of an oxide film of Al₂O₃oxidized aluminum. Accordingly, the anodic oxide film causes theopposite thermosetting resin to be worn out by frictional driving. Lossmarks may occur at the frictional contact face of the worn thermosettingresin. There has been the problem of an increase in the minimum voltagerequired to start the vibration actuator, resulting from the occurrenceof loss marks and transfer of the components lost from the thermosettingresin film to the opposite member.

The problem to be solved by the present invention is to provide avibration actuator which is easy to manufacture and has favorabledriving properties, and a lens barrel and camera provided with the same.

Means for Solving the Problems

The present invention solves the problem described above by thefollowing means.

In the first aspect of the invention, a vibration actuator is provided,which includes an oscillator configured to generate oscillations and arelative movement member which is in pressure contact with theoscillator configured to relatively move with respect to the oscillatordue to the oscillations. Of a contact face of the oscillator withrespect to the relative movement member and a contact face of therelative movement member with respect to the oscillator, at least one isa thermosetting resin film composed of a polyamide-imide resin and afluororesin and the other is an anodic oxide film.

In the second aspect of the invention, the vibration actuator accordingto the first aspect is provided, in which the thermosetting resin filmhas an indentation hardness of 0.1 to 0.3 GPa.

In the third aspect of the invention, a vibration actuator according tothe first or second aspect is provided, in which the anodic oxide filmincludes a hard anodic oxide film.

In the fourth aspect of the invention, a vibration actuator is provided,which includes an oscillator configured to generate oscillations and arelative movement member which is in pressure contact with theoscillator configured to relatively move with respect to the oscillatordue to the oscillations. Of a contact face of the oscillator withrespect to the relative movement member and a contact face of therelative movement member with respect to the oscillator at least one isa thermosetting resin film composed of a polyamide-imide resin and afluororesin and the other is a film having an indentation hardness of20000 to 30000 GPa.

In the fifth aspect of the invention, the vibration actuator accordingto the fourth aspect is provided, in which the thermosetting resin filmhas an indentation hardness of 01. to 0.3 GPa.

In the sixth aspect of the invention, the vibration actuator accordingto the fourth or fifth aspect is provided, in which the film includes ananodic oxide film.

In the seventh aspect of the invention, the vibration actuator accordingto any one of the fourth to sixth aspects is provided, in which theanodic oxide film includes a hard anodic oxide film.

In the eighth aspect of the invention, the vibration actuator accordingto any one of the first to seventh aspects is provided, in which thethermosetting resin includes a pigment.

In the ninth aspect of the invention, the vibration actuator accordingto the eighth aspect is provided, in which the hardness of the pigmentis 15000 to 50000 GPa.

In the tenth aspect of the invention, the vibration actuator accordingto the eighth or ninth aspect is provided, in which the pigment has aweight ratio of 20 to 50 with respect to 100 of the polyamide-imide.

In the eleventh aspect of the invention, the vibration actuatoraccording to any one of the first to tenth aspects is provided, in whicha work rate of indentation of the thermosetting resin film is 30% orless.

In the twelfth aspect of the invention, the vibration actuator accordingto any one of the first to eleventh aspects is provided, in which thefluororesin has a weight ratio of 20 to 50 with respect to 100 of thepolyamide-imide.

In the thirteenth aspect of the invention, a lens barrel is provided,which includes the vibration actuator according to any one of the firstto twelfth aspects.

In the fourteenth aspect of the invention, a camera is provided, whichincludes the vibration actuator according to any one of the first totwelfth aspects.

Effects of the Invention

According to the present invention, it is possible to provide avibration actuator which is easy to manufacture and has favorabledriving properties, and a lens barrel and camera provided with the same.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing showing a camera of the first embodiment.

FIG. 2 is a drawing showing an ultrasonic wave motor according to thefirst embodiment.

FIG. 3 is an enlarged drawing showing frictional contact faces of anelastic body and a moving body of the ultrasonic wave motor of the firstembodiment.

FIG. 4 is a drawing schematically showing the structure inside a resinfilm.

FIG. 5 is a cross sectional drawing showing an ultrasonic wave motor ofthe second embodiment.

EXPLANATION OF REFERENCE NUMERALS

-   -   1: camera    -   3: lens barrel    -   10, 20: ultrasonic wave motor    -   13, 23: oscillator    -   15, 25: moving body    -   18, 31: resin film    -   18 b: pigment    -   19, 32: anodic oxide film

PREFERRED MODE FOR CARRYING OUT THE INVENTION First Embodiment

FIG. 1 is a drawing showing a camera 1 of the first embodiment.

The camera 1 of the first embodiment is provided with a camera body 2having an imaging element 6 and a lens barrel 3. The lens barrel 3 is aninterchangeable lens which is mountable on and dismountable from thecamera body 2. It should be noted that the camera 1 of the presentembodiment shows an example where the lens barrel 3 is aninterchangeable lens. However, it is not limited to this, and it mayalternatively be possible that the lens barrel 3 is integrated with acamera body, for example.

The lens barrel 3 is provided with a lens 4, a cam tube 5, an ultrasonicwave motor 10, and the like. In the present embodiment, an ultrasonicwave motor is explained as an example of a vibration actuator. Theultrasonic wave motor 10 has an approximately annular shape, and isdisposed in the lens barrel 3 so that a direction of a central axis ofthe annulus substantially coincides with a direction of an optical axis(the direction shown by an arrow “A” in FIG. 1). The ultrasonic wavemotor 10 is used as a driving source to drive the lens 4 during afocusing action of the camera 1. A driving force provided by theultrasonic wave motor 10 is transmitted to the cam tube 5. A lens frame4 a of the lens 4 is cam-engaged with the cam tube 5. When the cam tube5 rotates about the optical axis by the driving force applied by theultrasonic wave motor 10, the lens 4 moves in the direction of theoptical axis to adjust focusing.

In FIG. 1, a lens group, (including lens 4) which is not shown in thedrawings and provided in the lens barrel 3, forms an image of aphotographic subject at an imaging face of the imaging element 6. Theimaging element 6 converts the formed image of the photographic subjectto an electric signal, which undergoes A/D conversion to be image data.

FIG. 2 is a drawing showing the ultrasonic wave motor 10 of the firstembodiment.

The ultrasonic wave motor 10 of the present embodiment is provided withan oscillator 13 including a piezoelectric body 11 and an elastic body12; a moving body 15; a flexible printed circuit board 14; a vibrationabsorbing member 16; a support 17 and the like.

The piezoelectric body 11 has the function of converting electric energyinto mechanical energy. In the present embodiment, a piezoelectricelement is used as the piezoelectric body 11, but an electrostrictiveelement may be alternatively used. The piezoelectric body 11 is fixed tothe support 17 provided at the lens barrel 3 via a vibration absorbingmember 16 such as felt or the like.

The piezoelectric body 11 has electrodes (not shown) formed thereon. Thepiezoelectric body 11 expands and contracts in accordance with a drivingsignal supplied from the flexible printed circuit board 14 electricallyconnected with the electrode portions, and causes the elastic body 12 tobe excited.

The elastic body 12 is a member which generates a progressive wave dueto the excitation caused by the piezoelectric body 11. The elastic body12 is formed of a ferroalloy such as stainless steel, Invar steel or thelike, having a high elastic modulus. The elastic body 12 of the presentembodiment is formed of SUS303.

The elastic body 12 is a substantially annular shaped member. Thepiezoelectric body 11 is adhered to one face of the elastic body 12 byan adhesive or the like having electrical conductivity.

A comb-tooth portion 12 a having a plurality of grooves 12 b is providedat the other face. End faces of the comb-tooth portion 12 a are contactfaces in pressure contact with the later described moving body 15. Themoving body 15 is rotationally driven by progressive waves generated atthis face. On the end faces of the comb-tooth portion 12 a, a resin film18 (refer to FIG. 3) having a polyamide-imide resin as the principalmaterial is formed. This resin film 18 will be explained in detaillater.

The moving body 15 is a substantially annular shaped member formed of ametal such as an aluminum alloy or the like. The moving body 15 of thepresent embodiment is formed of an aluminum alloy.

The moving body 15, with which the oscillator 13 (the elastic body 12)comes into contact, is frictionally driven by the progressive waves. Ananodic oxide film layer 19 is formed at a contact face of the movingbody 15, which is in contact with the oscillator 13 (refer to FIG. 3).

The flexible printed circuit board 14 is electrically connected withpredetermined electrodes of the piezoelectric body 11, and is a memberwhich supplies a driving signal to the piezoelectric body 11.

Further, a controller 108 which performs control of the camera 1 isconnected to the flexible printed circuit board 14. A temperature sensor109 is connected to the controller 108. The controller 108 adjusts thefrequency of the driving signal supplied to the piezoelectric body 11according to the detection performed by the temperature sensor 109 sothat the rotational speed of the ultrasonic wave motor 10 is maintainedconstant.

FIG. 3 is an enlarged drawing of the contact portion of the elastic body12 and the moving body 15 of the ultrasonic wave motor 10 of the firstembodiment. It should be noted that a portion of the cross section in aperipheral direction of the ultrasonic wave motor 10 is enlarged in FIG.3.

The resin film 18 is provided at the contact face (the end faces of thecomb-tooth portion 12 a) of the elastic body 12, which is in contactwith the moving body 15. The anodic oxide film layer 19 is provided atthe contact face of the moving body 15, which is in contact with theelastic body 12. Accordingly, the oscillator 13 and the moving body 15are in frictional contact with each other through the resin film 18 andthe anodic oxide film layer 19.

FIG. 4 is a cross sectional drawing schematically showing the resin film18 of the present embodiment. The resin film 18 of the presentembodiment is formed by applying a coating which has a polyamide-imideresin 18 c as the principal raw material, to whichpolytetrafluoroethylene (below referred to as PTFE) 18 a and a pigment18 b are added.

In the resin film 18 of the present embodiment, 30 parts by weight ofthe PTFE 18 a, and 30 parts by weight of a cobalt nickel pigment 18 bare mixed with respect to 100 parts by weight of the polyamide-imideresin 18 c.

Further, the resin film 18 is used with the surface ground toapproximately 10 μm. At this time the surface roughness Rz (JISB0601-2001) is 0.5 μm or less, and the film thickness after grinding is15 μm.

Further, unless otherwise stated, the amounts of the PTFE 18 a and thepigment 18 b are based on the weight of the polyamide-imide resin 18 cwhich is the principal component, and are shown as a ratio where theweight of the polyamide-imide resin is set to 100.

The resin film 18 having the polyamide-imide resin 18 c as the principalraw material is excellent compared with the case of using a coating ofanother resin in terms of: hardness; plastic deformation resistance;adhesion and peel strength; abrasion resistance; heat resistance;coating stability; formability; boiling water resistance; and the like.

Therefore, the resin film 18 formed of the polyamide-imide resin 18 cmixed with PTFE 18 a and the pigment 18 b provides expected effects suchas the following.

(1) Since the resin film 18 is harder compared to resin films formed ofother resins such as an epoxy resin or the like, it is possible toincrease the abrasion resistance and plastic deformation resistance ofthe contact face which is in contact with the moving body 15 (the anodicoxide film layer 19).(2) The peeling strength and the adherence of the resin film 18 to theoscillator 13 (the elastic body 12) will increase, and the durability ofthe resin film 18 will increases.(3) Since the heat resistance of the resin film 18 increases, it ispossible to prevent deformation of the resin film 18 due to frictionalheat generated when the ultrasonic wave motor 10 is in operation.(4) Since the water resistance of the resin film 18 increases, it ispossible to prevent chemical deterioration of the resin film 18 due toairborne moisture.

The PTFE 18 a included in the resin film 18 of the present embodiment isgranular, as shown in FIG. 4. The average of the diameter of the primarygrains of this PTFE 18 a is from 1 to 5 μm. It should be noted thatsince the film thickness of the resin film 18 of the present embodimentis 30 μm, PTFE 18 a having this size is used. However, it mayalternatively be that an appropriate average size of the PTFE 18 a isselectable according to the film thickness.

Since the PTFE 18 a having high lubrication qualities reduces thecoefficient of friction, it increases the starting performance at lowspeeds of the ultrasonic wave motor. In addition, since the PTFE 18 ahas a high water repellence, it may be expected that adhesion betweenthe resin film 18 and the anodic oxide film layer 19 is prevented underhigh temperature and high humidity conditions.

As shown in FIG. 4, the resin film 18 of the present embodiment includesthe pigment 18 b. If the hardness of the pigment included in the resinfilm 18 is less than 15000 GPa, it will easily adhere to the oppositematerial (the anodic oxide film layer 19) with which it is in contact.This is not preferable since the resin film 18 itself may be damaged bysuch an adhered pigment. Further, if greater than 50000 GPa, the pigmentis easily broken to roughen the surface of the resin film 18. This isnot preferable since the roughened resin material 18 may damage theopposite material (the anodic oxide film layer 19) with which the resinmaterial 18 is in contact. Accordingly, the hardness of the pigment ispreferably between 15000 and 50000 GPa.

The pigment 18 b of the present embodiment is cobalt nickel which has ahardness within the above described 15000 to 50000 GPa, and its averagegrain diameter is 1 to 3 μm. Since the inclusion of the pigment 18 bincreases the denseness of the resin film 18, the hardness and plasticdeformation resistance are increased, accordingly. Further, the pigment18 b transmits the heat generated by the frictional driving in thecontact face of the resin member 18 with the moving body 15 (the anodicoxide film layer 19) to the outside of the contact face. Accordingly,the pigment 18 prevents the heat to be confined inside the contact face,and has the effect of improving the driving efficiency.

Further, since the pigment 18 b increases the coefficient of frictionbetween the oscillator 13 and the moving body 15 (namely, thecoefficient of friction between the resin film 18 and the anodic oxidefilm layer 19), the holding torque and the maximum load torque willincrease.

This resin film 18 is formed according to the following process.

First, the contact face (the end face of the comb-tooth portion 12 a) ofthe elastic body 12 in contact with the moving body 15 is subject to adegreasing treatment. At this time, a surface roughening treatment suchas blast etching or the like may be carried out to further increase theadherence.

A solution is made by mixing PTFE 18 a, a cobalt nickel additive, andN-methylpyrrolidone with the polyamide-imide resin 18 c. This solutionis coated onto the frictional contact face of the elastic body 12, andafter preheating, is held at a temperature of about 250° C. for 20 to 60minutes to dry cure. After the curing, the surface of the resin film 18is polished and leveled using green carborundum or the like.

On the other hand, the anodic oxide film layer 19 is formed by applyingan anodic treatment to a surface of the moving body 15 made of analuminum alloy (A6061).

The oscillator 13 is formed by joining the piezoelectric body 11 to theelastic body 12 on which the resin film 18 is formed. The oscillator 13and moving body 15 are disposed such that the resin film 18 of theoscillator 13 and the anodic oxide film layer 19 of the moving body 15are in contact with each other, and the various members are assembled.The ultrasonic wave motor 10 is manufactured through these processes.

Here, ultrasonic wave motors 10 of Measurement Examples 1 to 13 withdiffering added amounts of the PTFE 18 a and the pigment 18 b additivesand the like with respect to the polyamide-imide resin 18 c (ratios withrespect to the weight of the polyamide-imide resin), and an ultrasonicwave motor 10 of Measurement Example 14 (Comparative Example) where anepoxy resin coating film is applied to a frictional contact face of anoscillator 13 were prepared. The minimum rotational speed at noiseoccurrence and performances associated with driving of the ultrasonicwave motors 10 were investigated, which include: the holding torque;maximum torque; minimum starting voltage; abrasion characteristics andthe like.

Further, the indentation hardness of the polyamide-imide resin film 18and the anodic oxide film layer 19 was measured. The indentationhardness represents the hardness obtained from the relationship betweenthe test force of a process of thrusting an indenter and the depth ofindentation, according to the stipulations of ISO 14577-1, “InstrumentedIndentation Test for Hardness”.

The work rate of indentation can also be obtained from aload-indentation depth curve. The work rate of indentation is defined as“an amount of work for an elastic deformation/(the amount of work forthe elastic deformation+an amount of work for a plastic deformation)”.

Table 1 is a table showing the measurement results of the holding torqueand the like for the ultrasonic wave motors 10 of Measurement Examples 1to 13 and for Comparative Example 14.

[Table 1]

The ultrasonic wave motors 10 of Measurement Examples 1 to 13 haveapproximately the same setup as the ultrasonic wave motor 10 of thepresent embodiment, other than differing in the added amounts of theadditives such as PTFE and the like, and the hardness. The ultrasonicwave motor of Measurement Example 3 corresponds to the ultrasonic wavemotor 10 of the present embodiment.

TABLE 1 Anodic oxide film Resin film HV converted Polyamid- IndentationIndentation Value Measurement imide PTFE Pigment Hardness Work Hardnessindentation Example weight Epoxy weight weight Gpa rate % Gpahardness/76.36 1 100 0 60 30 0.05 31 27000 354 2 100 0 50 30 0.1 27000354  3*1 100 0 30 30 0.2 25 27000 354 4 100 0 20 30 0.3 27000 354 5 1000 10 30 0.4 27000 354 6 100 0 30 30 0.2 16000 210 7 100 0 30 30 0.220000 262 8 100 0 30 30 0.2 30000 393 9 100 0 30 30 0.2 40000 524 10 100 0 30 60 0.4 27000 354 11  100 0 30 50 0.2 23 27000 354 12  100 0 3020 0.2 30 27000 354 13  100 0 30 10 0.1 27000 354 14  0 100 30 30 0.0538 27000 354 Rotational Resin film Min. speed at Amount of MeasurementHolding Max. starting noise abrasion Loss Example torque torque voltageoccurrence wear marks 1 Δ0.6 X0.5 ◯0.9 ◯1 or more Δ1.1 XYES 2 ◯0.9 ◯0.9◯0.9 ◯1 or more ◯1 ◯NO  3*1 ◯1 ◯1 ◯1 ◯1 ◯1 ◯NO 4 ◯ 1 or ◯1 or ◯1 ◯0.9 ◯1◯NO more more 5 ◯ 1 or ◯1 or Δ1.2 Δ0.7 Δ1.5 ◯NO more more 6 ◯0.9 ◯0.9Δ1.2 ◯1 ◯1 ◯NO 7 ◯1 ◯1 ◯1 ◯1 ◯1 ◯NO 8 ◯1 ◯1 ◯1 ◯1 ◯1 ◯NO 9 ◯1 ◯1 ◯1 Δ0.8Δ1.5 XYES 10  ◯ 1 or ◯1 or ◯1 Δ0.8 ◯1 ◯NO more more 11  ◯ 1 or ◯1 or ◯1◯1 ◯1 ◯NO more more 12  ◯1 ◯1 ◯1 ◯1 ◯1 ◯NO 13  ◯1 Δ0.8 ◯1 ◯1 Δ1.3 ◯NO14  Δ0.8 Δ0.7 Δ1.3 ◯1 Δ2 XYES *1EMBODIMENT STANDARD

Further, the ultrasonic wave motor of Measurement Example 14(Comparative Example) has approximately the same setup as the ultrasonicwave motor 10 of the present embodiment, other than differing in that anepoxy resin film instead of the polyamide resin film 18 is formed at thecontact face of the oscillator and the moving body. The ultrasonic wavemotor of this Measurement Example 14 is an example of the ultrasonicwave motors commonly used in the prior art.

The resin film 18 of the ultrasonic wave motor 10 of Measurement Example1 is now explained.

The resin film 18 of the ultrasonic wave motor 10 of Measurement Example1 is a resin film in which 60 parts by weight of PTFE and 30 parts byweight of cobalt nickel pigment are mixed with respect to 100 parts byweight of polyamide-imide. Carbon short fibers, silicon beads, andalumina particles are not added to the resin film of the ultrasonic wavemotor of Measurement Example 1.

Resin films 18 of the ultrasonic wave motors 10 of Measurement Examples2 to 5 are varied weight ratios of the PTFE 18 a, and the hardness ofeach resin film 18 differs, accordingly.

Resin films 18 of the ultrasonic wave motors 10 of Measurement Examples6 to 9 are the same as that of Measurement Example 3, but the hardnessof each of the anodic oxide films 19 differs, which are opposite to theresin films 18.

Resin films 18 of the ultrasonic wave motors 10 of Measurement Examples10 to 13 differ in the weight ratios of the pigments 18 b, and thehardness of each resin film 18 differs, accordingly.

A resin film 18 of Measurement Example 14 differs in that an epoxy resinis used as the principal component. In Measurement Example 14, the sameratios of the PTFE 18 a and the pigment 18 b are added as in MeasurementExample 3.

The holding torque shown in Table 1 represents the torque necessary tocause an ultrasonic wave motor 10 in a standstill to be driven at apredetermined driving voltage and rotational speed. A value of holdingtorque in FIG. 1 shows a ratio of the holding torque of an ultrasonicwave motor of each of the Measurement Examples with respect to theholding torque of the ultrasonic wave motor 10 of Measurement Example 3(Embodiment Standard), which is set as a standard value (1.0).

The value of the holding torque shown in Table 1 is preferably largefrom the viewpoints of the effect of improving the driving efficiencyand preventing rotation and the like of the moving body when not in use.If the value is greater than 0.9, it is useable as an ultrasonic wavemotor 10.

Next, the maximum torque shown in Table 1 is explained. The maximumtorque represents the maximum value of the loaded torque drivable by anultrasonic wave motor, namely, the maximum load torque. A value of themaximum torque shown in Table 1 is a ratio of the maximum load torque ofeach ultrasonic wave motor 10 with respect to the maximum load torque ofthe ultrasonic wave motor 10 of Measurement Example 3 (EmbodimentStandard), which is set as a standard value (1.0).

The value of the maximum torque shown in Table 1 is preferably 1.0 orgreater. If the value is greater than 0.9, it is within an allowablerange for the ultrasonic wave motor 10.

A minimum starting voltage represents a minimum voltage at which anultrasonic wave motor is drivable. The smaller this value is, it ispossible to drive the ultrasonic wave motor with the lower electricpower. If the value is 1.0 or less, it is within an allowable range foran ultrasonic wave motor 10.

A rotational speed at noise occurrence represents the smallestrotational speed at which a noise occurs when an ultrasonic wave motor10 is driven under predetermined driving conditions. Since theultrasonic wave motor 10 normally generates a noise at a rotationalspeed equal to or above the rotational speed at noise occurrence, it ispreferable that the rotational speed at noise occurrence is as large aspossible.

An amount of abrasion wear of a resin film 18 is measured and evaluatedas a depth of abrasion wear of an elastic body 12 for a case where anultrasonic wave motor 10 has been rotated 50000 revolutions at apredetermined load torque and rotational speed (load torque of 20 N*mmand rotational speed of 60 rpm). The depth of abrasion wear represents adifference in thickness of an oscillator 13 between before and after itsrotational driving, when the thickness of the oscillator 13 before itundergoes 50000 rotations is used as a reference value. The smaller thisabrasion depth, the smaller the amount of abrasion wear arising from thedriving is, and the more favorable the durability is.

In Table 1, the amount of abrasion wear of the driven ultrasonic wavemotor 10 of Measurement Example 14 (Comparative Example) has an abrasiondepth of approximately 3.0 μm. For Measurement Examples having an amountof abrasion wear of 1.0 μm or less which is considered to have favorabledurability, a circle mark is given in Table 1.

Loss marks of the resin film 18 are detachment marks of the resin filmcomponents of a depth of 2 μm or more, generated in the case of havingundergone the above 50000 rotations. Since an occurrence of the lossmarks causes the driving to be unstable, it is preferable that there areno loss marks.

The measured results for each of the ultrasonic wave motors 10 ofMeasurement Examples (Measurement Example 1 to Measurement Example 13)and Comparative Example (Measurement Example 14) are now explained.

First, in the ultrasonic wave motor 10 of the Comparative Example(Measurement Example 14), noise is not generated, but there is room forimprovement in the other areas of performance (holding torque, maximumtorque, minimum starting voltage, abrasion marks, and loss marks).

On the other hand, the holding torque, maximum torque, minimum startingvoltage, abrasion marks, loss marks, abrasion amount and low temperaturedriving characteristics for the ultrasonic wave motors 10 of theMeasurement Examples having the resin film 18 with the polyamide-imideresin 18 c as the principal component are preferable compared to theultrasonic wave motor 10 of Comparative Example (Measurement Example14).

Next, the resin films 18 of the ultrasonic wave motors 10 of MeasurementExamples 1 to 5 differ from each other only in the weight ratios of thePTFE 18 a. Accordingly, by comparing the driving performance of theultrasonic wave motors 10 of Measurement Examples 1 to 5, it is possibleto understand the influence exerted on the driving performance of anultrasonic wave motor 10 by the added weight of the PTFE 18 a.

When the weight of the PTFE is high, the coefficient of friction becomeslow and the torque is reduced, accordingly. Further, the PTFE 18 a hasgood releasability, thus the danger of its loss increases.

On the other hand, when the weight of PTFE is low, the coefficient offriction becomes high and the starting characteristic deteriorates,accordingly.

Measurement Examples 6 to 9 have the same resin film 18 as MeasurementExample 3, but the hardness of an anodic oxide film 19 of the oppositeface differs. If the anodic oxide film 19 is too hard, the problems ofabrasion and noise arise. If it is on the other hand too soft, theminimum starting voltage increases. This is because the relativerelationship of the hardness is changed, thus the friction increases.There is also a relationship between the elastic modulus and the motorcharacteristics (noise).

Measurement Examples 10 to 13 differ from each other only in the weightratios of the pigment 18 b of the resin film 18.

If the weight of the pigment 18 b is high, the resin film 18 becomeshard and noise is readily generated.

If the weight of the pigment 18 b is low, the strength of the resin film18 decreases, abrasion increases and the maximum load torque decreases.

For these results, it is understood that if the added weight of the PTFEis 20 to 50 and the added weight of the pigment is 20 to 50 with respectto the weight of 100 of the polyamide-imide resin 18 a, it will befavorable to satisfy the desired holding torque and maximum torque, todecrease the power requirement and to prevent noise and friction.

Second Embodiment

FIG. 5 is a cross sectional drawing showing an ultrasonic wave motor 20of the second embodiment.

The ultrasonic wave motor 20 of the second embodiment is provided in alens barrel 3 of a camera 1 in the same way as for the ultrasonic wavemotor 10 of the first embodiment, and is used as an actuator for drivinga lens 4 to perform a focusing operation. This ultrasonic wave motor 20differs from the first embodiment in that it is configured to transmit adriving force via a gear (not shown) to a cam tube (not shown) to causethe lens 4 held in the cam tube to be driven.

The ultrasonic wave motor 20 of the second embodiment is provided withan oscillator 23, a moving body 25, an output shaft 28, a pressingportion 29 and the like.

The oscillator 23 is a substantially annular shaped member having anelastic body 22, a piezoelectric body 21 that is joined to the elasticbody 22, and the like. The oscillator 23 generates a progressive wave bythe expansion and contraction of the piezoelectric body 21.

The elastic body 22 is a substantially annular shaped member formed of astainless steel, to one face of which the piezoelectric body 21 isjoined, and at the other face of which a comb-tooth portion 22 a formedby cutting a plurality of grooves in the circumferential direction isprovided. An end face of the comb-tooth portion 22 a is a contact facewhich is in pressure contact with the moving body 25 and causes thismoving body 25 to be driven by the progressive wave.

A contact face of the oscillator 23 in contact with the moving body 25has a resin film 31 formed thereon, in the same way as for theoscillator 13 shown in the first embodiment. The resin film 31 of thepresent embodiment is formed by applying a coating where 30 parts byweight of PTFE and 30 parts by weight of cobalt nickel pigment are mixedwith respect to 100 parts by weight of polyamide-imide resin. Further,the film thickness of the resin film 31 is 30 μm, and the surfaceroughness (JIS B0601-2001) is 0.5 μm.

The elastic body 22 has a flange 22 b shaped like a brim extending froman inner periphery of the elastic body 22 in a radial direction. Theelastic body 22 is supported at a support body 26 via this flange 22 b.

The piezoelectric body 21 has the function of converting electricalenergy into mechanical energy. In the present embodiment, in the sameway as in the first embodiment, a piezoelectric element is used as thepiezoelectric body 21, but it is alternatively possible to use anelectrostrictive element. This piezoelectric body 21 expands andcontracts according to a driving signal supplied from a flexible printedcircuit board 24 electrically connected with prescribed electrodesformed at the piezoelectric body 21, causing the elastic body 22 tovibrate.

A controller 208 which controls the camera provided with the ultrasonicwave motor 20 is connected to the flexible printed circuit board 24. Inthe present embodiment, a temperature sensor 209 is connected to thecontroller 208. The controller 208 adjusts the frequency of the drivingsignal to be supplied to the piezoelectric body 21 in accordance withthe detection results of the temperature sensor 209, such that therotational speed is maintained constant.

The moving body 25 in pressure contact with the oscillator 23 isrotationally driven by an elliptic motion generated by the progressivewave arising at the contact face (the end face of the comb-tooth portion22 a) of the oscillator 23.

The moving body 25 is a member which is formed of a light metal such asan aluminum alloy. The moving body 25 is fit at the output shaft 28. Themoving body 25 of the present embodiment is formed of an aluminum alloy,and an anodic oxide film 32 is formed on the contact face of the movingbody 25 with which the oscillator 23 is in contact.

Accordingly, the moving body 25 and the oscillator 23 are in frictionalcontact in such a manner that the anodic oxide film 32 and the resinfilm 31 are in contact with each other.

The output shaft 28 has a substantially cylindrical form. One end of theoutput shaft 28 is fitted to the moving body 25 via a rubber member 30,and the other end is rotatably mounted on the support body 26 via abearing 27. This output shaft 28 rotates integrally with the moving body25 and transmits the rotational motion of the moving body 25 to a drivenmember (not shown) such as a gear or the like.

The pressing portion 29 is a mechanism configured to apply pressure tothe oscillator 23 and the moving body 25. The pressing portion 29 isprovided with a spring 29 a, a pressing ring 29 b, a pressing ring 29 cand an E-ring 29 d. The spring 29 a generates a pressing force. Thepressing ring 29 b, which is disposed in contact with the bearing 27,presses one end of the spring 29 a. The pressing ring 29 c presses theother end of the spring 29 a. The E-ring 29 d which is inserted into agroove “I” formed at the output shaft 28 regulates the position of thepressing ring 29 c.

In the ultrasonic wave motor 20 as shown in the present embodiment, theresin film 31 is formed at the frictional contact face of the oscillator23 such that the abrasion wear is decreased, the noise is decreased, thedurability is increased, the driving performance is stabilized, and thestarting characteristics are improved.

Further, the ultrasonic wave motor 20 shown in the present embodimenthas the problem of heat generation because it is often produced as aminiaturized ultrasonic wave motor having a small diameter compared tothe ultrasonic wave motor shown in the first embodiment. However, theresin film 31 according to the present embodiment is excellent in heatradiation because of the use of the pigment. In addition, as theadherence of the coating of the polyamide-imide resin is favorable, itis possible to eliminate a process of applying primer or the like whichis necessary with epoxy resins or the like.

Modifications

Various modifications and variations are possible, without being limitedto the above explained embodiments.

(1) In each of the embodiments, the use of cobalt nickel has been shownas the pigment, for example. However, it is not limited to this, and itmay alternatively be possible to adopt carbon black or the like.

(2) In each of the embodiments, an example has been shown using hardanodic oxide as the anodic oxide. However, it is not limited to this,and it may alternatively be possible to adopt sulfuric acid anodic oxideor oxalic acid anodic oxide.

(3) In each of the embodiments, an example has been shown where theresin films 18, 31 are formed at the contact faces of the oscillators13, 23 (the end faces of the comb-tooth portion 12 a, 22 a). It is notlimited to this, and it may alternatively be possible that the resinfilms are formed at the contact faces of the moving bodies 15, 25.Further, it may alternatively possible that both of the contact faces ofthe oscillators 13, 23, and the contact faces of the moving bodies 15,25 have the resin films formed thereon.

Furthermore, it may alternatively be possible that a vibration actuatoris adopted in which the piezoelectric body and the moving body are infrictional contact instead of using an elastic body. In this case, itmay be sufficient that the resin film is formed at least one of thecontact face of the piezoelectric body facing the moving body, and thecontact face of the moving body facing the piezoelectric body.

(4) In each of the embodiments, stainless steel has been used as thematerial for forming the elastic bodies 12, 22. However, it mayalternatively be possible to use another iron material. For example,various types of ferrous materials such as S15C, S55C, SCr445, SNCM630and the like may be alternatively used, and phosphor bronze or aluminumalloys may be alternatively used.

(5) In each of the embodiments, an example has been shown where themoving bodies 15, 25 are formed of an aluminum alloy. However, it is notlimited to this, and an iron type material may be alternatively used.For example, various types of ferrous materials such as S15C, S55C,SCr445, SNCM630 and the like may be alternatively used. Further, it mayalternatively be possible to use a resin with high heat resistance suchas polyimide resin or PEEK (polyetheretherketone) resin or the like.

(6) In each of the embodiments, an example has been shown where PTFE isused as the fluororesin. However, it is not limited to this, and it mayalternatively be possible to select a suitable fluororesin. For example,it may be possible to list up: PFA(tetrafluoroethylene-perfluoroalkylvinyl ether copolymer), FEP(tetrafluoroethylene-hexafluoropropylene copolymer), PCTFE(polychloro-trifluoroethylene copolymer), ETFE (ethylenetetrafluoroethylene copolymer), ECTFE (ethylene chlorotrifluoroethylenecopolymer), PVDF (polyvinylidene fluoride), PVF (polyvinylfluoride) andthe like.

(7) In each of the embodiments, an example has been shown of anultrasonic wave motor where the moving bodies 15, 25 are rotationallydriven. However, it is not limited to this, and it may alternatively bepossible to adopt a linear type vibration actuator where the moving bodyis driven in a straight line. Further, in each of the embodiments, anexample has been given of a rotating type (cylindrical) ultrasonic wavemotor where the moving bodies 15, 25 are rotationally driven. The reasonfor this is that since this type of ultrasonic wave motor may oftencause a problem of adhesion, it is possible to obtain a large effect ifthe present invention is applied to.

(8) In each of the embodiments, an explanation has been given for anexample of an ultrasonic wave motor using oscillations in the ultrasonicrange. However, it is alternatively be possible to adopt a vibrationactuator using oscillations outside of the ultrasonic region.

(9) In each of the embodiments, an example has been shown where theultrasonic wave motors 10, 20 are used as an actuator for performing afocusing operation of a lens barrel of a camera. However, it is notlimited to this, and it may alternatively be possible that they are usedas an actuator for performing a zooming operation of a lens barrel.Further, it may alternatively be possible to use the ultrasonic wavemotors 10, 20 as an actuator of a copy machine or the like, a drivingportion of a steering wheel tilt device or a headrest of an automobileor the like.

Further, the embodiments and modifications may be used in appropriatecombinations, but detailed explanations of such are omitted. Further,the present invention is not limited by the above explained embodiments.

1. A vibration actuator comprising: an oscillator configured to generate oscillations, and a relative movement member which is in pressure contact with the oscillator configured to relatively move with respect to the oscillator due to the oscillations, wherein of a contact face of the oscillator with respect to the relative movement member and a contact face of the relative movement member with respect to the oscillator at least one is a thermosetting resin film composed of a polyamide-imide resin and a fluororesin and the other is an anodic oxide film. 